1. FIELD OF THE INVENTION
The present invention relates to structure of a clamping apparatus of a plate for a printing machine, and more specifically, to a clamping apparatus for a plate for a printing machine which can apply adequate tension to the plate depending on the materials of the plate.
2. DESCRIPTION OF THE PRIOR ART
Generally, in order to carry out printing with offset printing machines, an adequate amount of ink and dampening solution are supplied to a plate which is rolled around a plate cylinder and fitted thereon. A clamping apparatus is used for fitting the plate tightly on a cylinder surface of the plate cylinder. The plate is fitted on the cylinder surface of the plate cylinder to prevent a shear in printing or other failures in printing when the plate is not fitted tightly on the cylinder surface.
The structure and operation of conventional clamping apparatuses is described hereunder.
FIG. 13 is a sectional view showing a clamping apparatus 80 for fitting a plate on the cylinder surface of the plate cylinder. One edge (a leading edge side) of the plate 15 is clamped on the plate cylinder 30, and then the plate 15 is rolled around the cylinder surface of the plate cylinder 30. Thereafter, the other edge (a tail edge side) of the plate 15 is clamped by a clamping unit 20 provided on the tail edge side 35 of the plate cylinder 30. A plurality of adjustment bolts 22 are screwed into the clamping unit 20 in the same direction as a shaft of the plate cylinder 30. The clamping unit 20 is moved in the direction of arrow 200 as a result of pointed ends 22S of the adjustment bolts 22 contacting inner wall 30S of the tail edge side 35 when the adjustment bolts 22 are screwed into the clamping unit 20 to a certain depth.
In this way, the plate 15 clamped by the clamping unit 20 is pulled in the direction of the arrow 200 and the plate 15 is fitted on the cylinder surface of the plate cylinder 30. As indicated, the plate 15 is fitted tightly on the plate cylinder by screwing each of the adjustment bolts 22. On the contrary, each of the adjustment bolts is unscrewed in order to loosen the fixture of the plate 15 on the cylinder surface of the plate cylinder 30. The fixture of the plate 15 on the cylinder surface of the plate cylinder 30 is loosened as a result of moving the clamping unit 20 in the direction of arrow 300.
Further, there is conventional clamping apparatus which uses a plurality of coil springs between a side wall formed in the plate cylinder and the clamping unit instead of the adjustment bolts 22. The plate is fitted tightly on the cylinder surface of the plate cylinder by pulling the plate as a result of moving the clamping unit with spring force of the coil springs.
In addition, another conventional clamping apparatus is shown in FIG. 14. A clamping unit 40 is provided on the tail edge side of the plate cylinder 60, and the tail edge side part of the plate 19 is clamped by the clamping unit 40. A plurality of coil springs 45 are provided between the inner wall of the plate cylinder 60 and the clamping unit 40. The clamping unit 40 which clamps the plate 19 is pushed in the direction of arrow 150 by the spring force of the coil springs 45.
Also, a stopper 28 is provided on the plate cylinder 60, and a plurality of stopper screws 38 are screwed and pass through the stopper 28. Each of the stopper screws 38 is disposed in the same direction as the shaft of the plate cylinder 60. Pointed ends of the stopper screws 38 are contacted with the clamping unit 40. In other words, movement of the clamping unit 40 in the direction of the arrow 150 is restricted by the stopper screws 38 each of which is screwed into the stopper 28.
Each of the stopper screws 38 is loosened when the plate 19 is fitted tightly on the cylinder surface of the plate cylinder 60 by using the clamping unit 160. The plate 19 is fitted tightly on the cylinder surface of the plate cylinder 60 by pulling the plate 19 which is clamped by the clamping unit 40 as a result of moving the clamping unit 40 in the direction of the arrow 150 with the spring force of the coil springs 45 and the plate 19 can be fitted more tightly on the cylinder surface of the plate cylinder 60 with certain reliability by loosening each of the stopper screws 38.
On the other hand, each of the stopper screws 38 is screwed further in order to loosen the fixture of the plate 19 on the cylinder surface of the plate cylinder 60. By doing that, however, the fixture of the plate 19 on the cylinder surface of the plate cylinder 60 is loosened as a result of moving the clamping unit 40 in the direction of the arrow 190.
The conventional clamping apparatuses described above have the following problems to be resolved. Plates for printing machines are made of several different materials such as aluminum, resins, papers and so on. It is necessary to adjust tension for fitting these plates on the cylinder surface of the plate cylinder depending on the materials of the plates.
In the clamping apparatus 80 shown in FIG. 13, the moving distance of the clamping unit 20 can be adjusted by the amount of screwing done by each of the adjustment bolts 22. As a result, the tension applied to the plate 15 can be adjusted. Although the tension can be adjusted by the clamping apparatus, each of the adjustment bolts 22 has to be screwed on a one by one basis. In this way, adjustment of the tension takes much time and much work.
However, the tension applied to the plate can not be adjusted in conventional clamping apparatus which are equipped with coil springs instead of adjustment bolts 22. The coil springs can only apply uniform tension to the clamping unit. It is not possible for the clamping apparatus to apply tension to the clamping unit depending on the materials of the plates.
For instance, a plate which requires high tension for fitting can not be fitted tightly on the cylinder surface of the plate cylinder when coil springs having lower spring force than the tension required by the plate are provided to the clamping apparatus. Insufficient tension is applied to the plate. On the other hand, a plate which requires low tension for fitting may be damaged when coil springs having higher spring force than the tension required by the plate are provided to the clamping apparatus. Too much tension is applied to the plate.
Further, tension applied to the plate 19 can be adjusted in the clamping apparatus shown in FIG. 14 because the moving distance of the clamping unit 40 is adjusted by the amount of screwing done by each of the stopper screws 38. Although, the tension can be adjusted by the clamping apparatus, each of the stopper screws 38 has to be screwed on a one by one basis. In this way, adjustment of the tension to the plate 19 takes much time and much work similar to the clamping apparatus 80 shown in FIG. 13.